How can I make my interior scene better lighted?
As I said, there are techniques at your disposal to reduce noise (and by extension, render time) that don't involve relinquishing your shadows.  Here's an example showing how much Clamping actually affects shadow exposure.  I've used the Denoising filter (for simplicity) included with Blender 2.79 Candidate but there are more effective and more flexible ways of controlling noise as well.

Denoising settings for this render:



Notice also the wood texture outside the window, with an Indirect Clamping value as extreme as 1.00, it's affected as well, since it's technically not Direct light.





Full size (Click to enlarge):